Chromatography of polyolefin polymers

ABSTRACT

A method and apparatus for chromatography of a polyolefin polymer by flowing a solution of the polyolefin polymer through liquid flowing through a graphitic carbon liquid chromatography stationary phase. The method can be used to determine the monomer to comonomer ratio of a polyolefin copolymer such as a copolymer of ethylene and 1-octene or a copolymer of propylene and ethylene.

REFERENCE TO RELATED APPLICATIONS

This present application is a Continuation of U.S. application Ser. No.12/572,313, filed Oct. 2, 2009, now U.S. Pat. No. 8,076,147, and whichis a 35 U.S.C. §371 of International Application No. PCT/US09/059,261,filed Oct. 1, 2009, which claims the benefit of U.S. Provisional61/195,326 filed on Oct. 6, 2008 and U.S. Provisional No. 61/181,015filed on May 26, 2009, and fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

The disclosed invention is in the field of liquid chromatography. Liquidchromatography is used by the art to analyze polymers with regard tomolecular size by Size Exclusion Chromatography (SEC) and with regard tochemical composition by High Performance Liquid Chromatography (HPLC).This disclosure relates to HPLC analysis of polymers with regard tochemical composition.

Polyolefin polymers (such as polymers and copolymers comprisingpolymerized ethylene monomer and/or propylene monomer) have long beenanalyzed with regard to chemical composition distribution by temperaturerising elution fractionation (TREF) and crystallization analysisfractionation (CRYSTAF). However, neither TREF nor CRYSTAF can be usedto analyze amorphous polyolefin polymers. Furthermore, both TREF andCRYSTAF require a relatively long analysis time. Therefore, the artturned to HPLC in an attempt to reduce analysis time and to expand thescope of analysis to amorphous polymers. Macko et al. apparently werethe first to do so in 2003 by studying the retention of polyethylenestandards on silica and zeolite stationary phases (J. Chrom. A, 1002(2003) 55). Wang, et al. studied the retention of polyethylene andpolypropylene by zeolites in 2005 (Macromolecules, V. 38, No. 25 (2005)10341). Heinz and Pasch used a silica stationary phase to analyzepolyethylene—polypropylene blends by HPLC (Polymer 46 (2005) 12040).Albrecht, et al., used a silica stationary phase to analyzeethylene—vinyl acetate copolymers by HPLC (Macromolecules 2007, 40,5545). Albrecht, et al., used a silica stationary phase to analyzeethylene—propylene copolymers by HPLC (Macromol. Symp. 2007, 257, 46). Aremaining problem for the HPLC analysis of polyolefin polymers is thelimited separation efficiency obtained by the prior art methods.

SUMMARY OF THE INVENTION

A primary benefit of this disclosure is the provision of an HPLC methodhaving improved separation efficiency for the analysis of a polyolefinpolymer. More specifically, in one embodiment this disclosure is amethod for chromatography of a polyolefin polymer, comprising the stepof: introducing a solution of the polyolefin polymer into a liquidmobile phase flowing through a liquid chromatography stationary phase,the liquid chromatography stationary phase comprising graphitic carbon,the polyolefin polymer emerging from the liquid chromatographystationary phase with a retention factor greater than zero.

In another embodiment, this disclosure is an improved liquidchromatography method comprising the step of introducing a solution ofthe polyolefin polymer into a liquid mobile phase flowing through aliquid chromatography stationary phase, the polyolefin polymer emergingfrom the liquid chromatography stationary phase with a retention factorgreater than zero the improvement comprising the liquid chromatographystationary phase comprising graphitic carbon.

In another embodiment, this disclosure is a method for determining themonomer to comonomer ratio of a copolymer consisting essentially ofethylene and an alpha olefin comonomer, comprising the steps of: (a)flowing a liquid mobile phase into contact with a liquid chromatographystationary phase comprising graphitic carbon to produce an effluentstream of liquid mobile phase from the stationary phase; (b) introducinga solution of the copolymer into the liquid mobile phase so that thecopolymer emerges in the effluent stream with a retention factor thatvaries as a mathematical function of the monomer to comonomer ratio ofthe copolymer.

In another embodiment, this disclosure is a method for determining themonomer to comonomer ratio of a copolymer consisting essentially ofpropylene and an alpha olefin comonomer, comprising the steps of: (a)flowing a liquid mobile phase into contact with a liquid chromatographystationary phase comprising graphitic carbon to produce an effluentstream of liquid mobile phase from the stationary phase; (b) introducinga solution of the copolymer into the liquid mobile phase so that thecopolymer emerges in the effluent stream with a retention factor thatvaries as a mathematical function of the monomer to comonomer ratio ofthe copolymer.

In another embodiment, this disclosure is an improved chromatographicfractionation technique for separating atactic and isotacticpolypropylene from syndiotactic polypropylene.

In yet another embodiment, the invention is an apparatus for determiningthe monomer to comonomer ratio of a copolymer, especially a copolymer ofethylene or propylene and at least one C3-C20 alpha-olefin. Theapparatus comprises a high temperature liquid chromatography unit (e.g.,a WATERS GPCV2000 or a Polymer Laboraties 210 or 220 equipped with agraphitic carbon liquid chromatography column (such as HYPERCARB brand)and a pump.

In another embodiment, the invention is a method of establishing and/ormaintaining quality control of a polymerization product, such as anethylene based polymer or a propylene based polymer.

In still another embodiment, the invention is a method of removingmolecular components having a specific comonomer content in a commercialpolymerization process for polyolefin production to produce a productwith a narrower comonomer distribution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a theorized HPLC chromatogram depicting the elution of aretained component;

FIG. 2 shows a typical HPLC system;

FIG. 3 is an overlay of chromatograms of polymers of 1-octene, ethyleneand copolymers of various ratios of 1-octene and ethylene using adisclosed graphitic carbon stationary phase;

FIG. 4 is an overlay of chromatograms of polymers of propylene, ethyleneand copolymers of various ratios of propylene and ethylene using adisclosed graphitic carbon stationary phase;

FIG. 5 is an overlay of chromatograms of polymers of 1-octene, ethyleneand copolymers of various ratios of 1-octene and ethylene using adisclosed graphitic carbon stationary phase;

FIG. 6. is an overlay of three polypropylenes with differenttacticities.

FIG. 7 is an overlay of chromatograms of polymers of 1-octene, ethyleneand copolymers of various ratios of 1-octene and ethylene using a priorart silica stationary phase;

FIG. 8 is an overlay of chromatograms of polymers of propylene, ethyleneand copolymers of various ratios of propylene and ethylene using a priorart silica stationary phase; and

FIG. 9 is a calibration curve related to the chromatograms shown in FIG.3.

DETAILED DESCRIPTION

The theorized HPLC chromatogram shown in FIG. 1 depicts the elution ofCOMPONENT A at an elution volume peaking at Vr. A low molecular weightunretained component eluting from the stationary phase would elute atV₀. The retention factor (k) for COMPONENT A is (Vr−V₀)÷V₀.

FIG. 2 shows a typical HPLC system 10 of the prior art that includes aneluant reservoir 11 filled with a liquid mobile phase 12 or when agradient system is used multiple reservoirs would be needed. The liquidmobile phase 12 is pumped by pump 13 through injection valve 14 intochromatography column 19. The chromatography column 19 is filled withliquid chromatography stationary phase 20 comprised in a granularpacking. The liquid mobile phase 12 flows through the liquidchromatography stationary phase 20, through detector 21 and into usedeluant reservoir 22 as used liquid mobile phase 23. A solution of asample to be analyzed is contained in syringe 15 and dispensed throughsample volume loop 16 of injection valve 14 in its sample load positioninto excess sample reservoir 17 as excess sample 18. When injectionvalve 14 is placed in its sample inject position, liquid mobile phase 12is flowed through the sample volume loop 16 to flow the injected sampleinto the chromatography column 19. If a component of the injected sampleis retained by the stationary phase 20 so that the component flowsthrough the chromatography column 19 at a slower rate than the mobilephase 12, then the component will emerge from the chromatography column19 with a retention factor greater than zero to be detected by detector21. A general purpose digital computer 24 is in electrical communicationwith detector 21 and is programmed to manipulate the signal from thedetector 21 to provide, for example, a chromatogram of the injectedsample.

This disclosure is a method for chromatography of a polyolefin polymer,comprising the step of: introducing a solution of the polyolefin polymerinto a liquid flowing through a liquid chromatography stationary phase,the liquid chromatography stationary phase comprising graphitic carbon,the polyolefin polymer emerging from the liquid chromatographystationary phase with a retention factor greater than zero. Theimprovement of this disclosure centers on the use of a liquidchromatography stationary phase comprising graphitic carbon.

This disclosure is also a method for determining the monomer tocomonomer ratio of a copolymer consisting essentially of ethylene orpropylene and an alpha olefin comonomer, comprising the steps of: (a)flowing a liquid mobile phase into contact with a liquid chromatographystationary phase comprising graphitic carbon to produce an effluentstream of liquid mobile phase from the stationary phase; (b) introducinga solution of the copolymer into the liquid mobile phase so that thecopolymer emerges in the effluent stream with a retention factor thatvaries as a mathematical function of the monomer to comonomer ratio ofthe copolymer.

The term “polyolefin polymer” in this disclosure is defined as allpolymers and copolymers (including high pressure low densitypolyethylene (LDPE), heterogeneous polymers, random, block, and graftpolymers, interpolymers and copolymers) comprising one or morepolymerized monomers selected from the group consisting of ethylene, analpha olefin having from 3-20 carbon atoms (such as 1-propylene,1-butene, 1-hexene, 1-heptene and 1-octene), 4-methyl-1-pentene, and/oracetylenically unsaturated monomers having from 2-20 carbons, and/ordiolefins having from 4-18 carbons and any other monomer used in the artto modify the density of a polymer. Heterogeneous polymers includeZiegler-Natta polymerized polymers such as LLDPE and HDPE and includeproducts such as DOWLEX™ made by The Dow Chemical Company. The randomcopolymers include those polymerized using metallocene or constrainedgeometry catalyst technology and include polymers such as AFFINITY™ andENGAGE™, both available from The Dow Chemical Company, and EXACT™,available from Exxon-Mobil. Methods for polymerizing these randomcopolymers are well known in the art and include those described in U.S.Pat. Nos. 5,272,236 and 5,278,272. The block coplymers include thosepolymerized using chain shuttling technology and two catalyst species,such as is disclosed in U.S. Pat. No. 7,355,089, and include polymerssuch as INFUSE™ Olefin Block Copolymers made by The Dow ChemicalCompany. In addition the term “polyolefin polymer” in this disclosure isdefined as a polymer having an average molecular weight, as determinedby light scattering, greater than 1,000 grams per mole (preferablygreater than 2,000 grams per mole and more preferably greater than 4,000grams per mole). The polyolefin polymer can be a copolymer consistingessentially of polymerized ethylene monomer and a polymerized alphaolefin monomer such as 1-octene. The polyolefin polymer can be acopolymer consisting essentially of polymerized propylene monomer and apolymerized alpha olefin monomer such as ethylene. Such propylene basedpolymers include homopolymer polypropylene, impact propylene basedcopolymers, and random propylene based copolymers. Other morespecialized polymers also benefit from the method and apparatusdisclosed herein and include ethylene/acrylic acid copolymers,ethylene/vinyl acetate copolymers and ethylene/styrene interpolymers,halogenated polymers, and polymers containing maleic anhydride moeities.

In most applications the temperature of the solution of the polyolefinpolymer, the temperature of the liquid chromatography stationary phaseand the temperature of the detector will be controlled at an elevatedtemperature to increase the solubility of the polyolefin polymer, e.g.,to render the polyolefin polymer soluble. The concentration of thepolyolefin polymer in the solution of polyolefin polymer is preferablygreater than 0.1 milligrams per milliliter of solution, especiallygreater than 2 mg/mL. The solvent used for the solution of thepolyolefin polymer is preferably decanol when the polyolefin polymer ispolyethylene or polypropylene. Any suitable liquid mobile phase can beused in the method of this disclosure. A gradient composition mobilephase is preferred in the method of this disclosure. The temperature ofthe liquid chromatography stationary phase can be increased during themethod of this disclosure. A mobile phase having no aliphatic hydrogencontent (such as 1,2,4-trichloro benzene) facilitates the use of aninfrared detector for the method of this disclosure.

Any liquid chromatography stationary phase that comprises graphiticcarbon can be used in the method of this disclosure. The term “graphiticcarbon” in this disclosure is defined as all varieties of materialscomprising the element carbon in the allotropic form of graphiteirrespective of the presence of structural defects if thethree-dimensional hexagonal crystalline long-range order of graphite canbe detected in the material by diffraction methods (such as X-raydiffraction spectroscopy) independent of the volume fraction and thehomogeneity of distribution of such crystalline domains. Carbonnanotubes and carbon “buckeyballs” are examples of forms of graphiticcarbon that are useful in the method of this disclosure. Preferably, theliquid chromatography stationary phase consists essentially of graphiticcarbon, especially porous graphitic carbon. The graphitic carbon isusually packed into columns and comprises flat sheets of hexagonallyarranged carbon atoms at the molecular level. The graphitic carbondesirably has a particle size of from about 1 to about 10 microns,preferably an average particle size of about 3 microns, or 5 microns or7 microns, and preferably has an average pore size of about 200 to about300 Angstroms, more preferably an average pore size of about 250Angstroms. The internal surface of the graphitic carbon has an area ofabout 100 to about 140 square meters/gram, preferably about 120 squaremeters/gram. The length of the columns is typically from about 30 mm toabout 100 mm and can have a diameter of from about 2 mm to about 5 mm.An example of a commercially available liquid chromatography stationaryphase that consists essentially of graphitic carbon is believed toinclude the HYPERCARB brand HPLC column from Thermo Scientific, WalthamMass. An example of a commercially available liquid chromatographystationary phase that comprises graphitic carbon is believed include theDISCOVERY ZR-CARBON brand HPLC column from Sigma Aldrich, St. Louis, Mo.Leboda, et al, Materials Chemistry and Physics 55 (1998) pages 1-29, isa literature review of HPLC carbon adsorbents.

The method of this disclosure can be coupled, on or off line, with otheranalytical methods. For example, the effluent from an SEC columncontaining an ethylene 1-octene polyolefin copolymer of a selectedmolecular size can be analyzed by the method of this disclosure todetermine the ratio of ethylene to 1-octene of the copolymer of theselected molecular size.

The method of this disclosure could be scaled up to include large scalefractionations of many grams or many pounds of polymer by scaling up thesize of the apparatus and the graphitic column.

In addition this disclosure could include a temperature gradient inaddition to or instead of a solvent gradient as a way to perform thefractionation.

In addition this disclosure could include a fractionation in acommercial process to refine the purity of the comonomer distribution ofthe commercial product.

A preferred set of operating conditions for this disclosure are anEGMBE/TCB gradient with an autos ampler and injector temperature ofabout 160° C. and a column temperature of about 140° C. Anotherpreferred set of operating conditions for this disclosure are adecanol/TCB gradient with an autosampler, injector, and columntemperature of about 175° C.

Example 1

An HPLC system is assembled using a 4.6×100 mm, 5 micrometer packingsize, 250 Å pore size, HYPERCARB brand liquid chromatography column, agradient composition mobile phase at a flow rate of 1.0 milliliters perminute having an initial composition of 100 vol. % ethylene glycol monobutyl ether for 3 minutes after injection and then a 15 minute lineargradient composition change to 100 vol. % 1,2,4-trichloro benzenefollowed by a 3 minute hold at 100 vol. % 1,2,4-trichloro benzene, aninjection volume of 10 micro liters, a sample concentration of 2milligrams of polymer per milliliter of 160° C. decanol, a columntemperature of 140° C., an injection valve temperature of 160° C., aPolymer Laboratories (Amherst, Mass.) ELS-1000 evaporative lightscattering detector operated with a gas flow of 1.4 liters per minute, anebulation temperature of 200° C. and an evaporation temperature of 250°C. Ten samples of copolymers of various mole ratios of polymerizedethylene and 1-octene monomers are prepared and chromatographed as shownin FIG. 3. The retention factors shown in FIG. 3 vary as a mathematicalfunction of the monomer to comonomer ratio of the copolymer with 0 molepercent 1-octene (100 mole percent ethylene) having the highestretention factor and 100 mole percent 1-octene having the lowestretention factor. Such mathematical function can be expressed as thecalibration curve shown in FIG. 9. Such mathematical function can beincorporated into the program of a general purpose digital computer toautomatically determine the ratio.

Example 2

An HPLC system is assembled using a 4.6×100 mm, 5 micrometer packingsize, 250 Å pore size, HYPERCARB brand liquid chromatography column, agradient composition mobile phase at a flow rate of 1.0 milliliters perminute having an initial composition of 100 vol. % ethylene glycol monobutyl ether for 3 minutes after injection and then a 15 minute lineargradient composition change to 100 vol. % 1,2,4-trichloro benzenefollowed by a 3 minute hold at 100 vol. % 1,2,4-trichloro benzene, aninjection volume of 10 micro liters, a sample concentration of 2milligrams of polymer per milliliter of 160° C. decanol, a columntemperature of 140° C., an injection valve temperature of 160° C., aPolymer Laboratories (Amherst, Mass.) ELS-1000 evaporative lightscattering detector operated with a gas flow of 1.4 liters per minute, anebulation temperature of 200° C. and an evaporation temperature of 250°C. Ten samples of copolymers of various mole ratios of polymerizedethylene and propylene monomers are prepared and chromatographed asshown in FIG. 4. The retention factors shown in FIG. 4 vary as amathematical function of the monomer to comonomer ratio of the copolymerwith 100 mole percent propylene (0 mole percent ethylene) having thelowest retention factor and 0 mole percent propylene (100 mole percentethylene) having the highest retention factor.

Example 3

An HPLC system is assembled using a 4.6×50 mm, 5 micrometer packingsize, DISCOVERY ZR-CARBON brand liquid chromatography column, a gradientcomposition mobile phase at a flow rate of 1.0 milliliters per minutehaving an initial composition of 100 vol. % ethylene glycol mono butylether for 3 minutes after injection and then a 15 minute linear gradientcomposition change to 100 vol. % 1,2,4-trichloro benzene followed by a 3minute hold at 100 vol. % 1,2,4-trichloro benzene, an injection volumeof 10 microliters, a sample concentration of 2 milligrams of polymer permilliliter of 160° C. decanol, a column temperature of 140° C., aninjection valve temperature of 160° C., a Polymer Laboratories (Amherst,Mass.) ELS-1000 evaporative light scattering detector operated with agas flow of 1.4 liters per minute, a nebulation temperature of 200° C.and an evaporation temperature of 250° C. Ten samples of copolymers ofvarious mole ratios of polymerized ethylene and 1-octene monomers areprepared and chromatographed as shown in FIG. 5. The retention factorsshown in FIG. 5 vary as a mathematical function of the monomer tocomonomer ratio of the copolymer but with a functionality that is not asgood as that shown in FIG. 3 because it appears that some samples havingdifferent ratios will have the same retention factor.

Example 4

An HPLC system is assembled using a 4.6×100 mm, 5 micrometer packingsize, 250 Å pore size, HYPERCARB brand liquid chromatography column, agradient composition mobile phase at a flow rate of 1.0 milliliters perminute having an initial composition of 100 vol. % ethylene glycol monobutyl ether for 3 minutes after injection and then a 15 minute lineargradient composition change to 100 vol. % 1,2,4-trichloro benzenefollowed by a 3 minute hold at 100 vol. % 1,2,4-trichloro benzene, aninjection volume of 10 micro liters, a sample concentration of 2milligrams of polymer per milliliter of 160° C. decanol, a columntemperature of 140° C., an injection valve temperature of 160° C., aPolymer Laboratories (Amherst, Mass.) ELS-1000 evaporative lightscattering detector operated with a gas flow of 1.4 liters per minute, anebulation temperature of 200° C. and an evaporation temperature of 250°C. Three samples of polypropylene of varying tacticity are prepared andchromatographed in FIG. 6 The retention of the polymers varies as afunction of tacticity. Atactic and isotactic have a similar retentiontime, while syndiotactic is retained.

Comparative Example 1

An HPLC system is assembled using a 4.6×250 mm, 5 micrometer packingsize, 300 Å pore size Macherey Nagel silica liquid chromatography column(Macherey Nagel GmbH & Co. KG, Düren, Germany), a gradient compositionmobile phase at a flow rate of 1.0 milliliters per minute having aninitial composition of 100 vol. % ethylene glycol mono butyl ether for 3minutes after injection and then a 15 minute linear gradient compositionchange to 100 vol. % 1,2,4-trichloro benzene followed by a 3 minute holdat 100 vol. % 1,2,4-trichloro benzene, an injection volume of 10 microliters, a sample concentration of 2 milligrams of polymer per milliliterof 160° C. decanol, a column temperature of 140° C., an injection valvetemperature of 160° C., a Polymer Laboratories (Amherst Mass.) ELS-1000evaporative light scattering detector operated with a gas flow of 1.4liters per minute, a nebulation temperature of 200° C. and anevaporation temperature of 250° C. Ten samples of copolymers of variousmole ratios of polymerized ethylene and 1-octene monomers are preparedand chromatographed as shown in FIG. 7. A comparison of thechromatograms shown in FIG. 7 with the chromatograms shown in FIG. 3demonstrates the superior separation efficiency obtained using thegraphitic carbon stationary phase of this disclosure in comparison tothe use of a silica stationary phase of the prior art. In addition,artifact peaks are observed early in the chromatograms of FIG. 7 between1.5 and 3.5 minutes, especially for the sample containing 100 molepercent 1-octene.

Comparative Example 2

An HPLC system is assembled using a 4.6×250 mm, 5 micrometer packingsize, 300 Å pore size Macherey Nagel silica liquid chromatography column(Macherey Nagel GmbH & Co. KG, Düren, Germany), a gradient compositionmobile phase at a flow rate of 1.0 milliliters per minute having aninitial composition of 100 vol. % ethylene glycol mono butyl ether for 3minutes after injection and then a 15 minute linear gradient compositionchange to 100 vol. % 1,2,4-trichloro benzene followed by a 3 minute holdat 100 vol. % 1,2,4-trichloro benzene, an injection volume of 10 microliters, a sample concentration of 2 milligrams of polymer per milliliterof 160° C. decanol, a column temperature of 140° C., an injection valvetemperature of 160° C., a Polymer Laboratories (Amherst Mass.) ELS-1000evaporative light scattering detector operated with a gas flow of 1.4liters per minute, a nebulation temperature of 200° C. and anevaporation temperature of 250° C. Ten samples of copolymers of variousmole ratios of polymerized ethylene and propylene monomers are preparedand chromatographed as shown in FIG. 8. A comparison of thechromatograms shown in FIG. 8 with the chromatograms shown in FIG. 4demonstrates the superior separation efficiency obtained using thegraphitic carbon stationary phase of this disclosure in comparison tothe use of a silica stationary phase of the prior art.

What is claimed is:
 1. A method for chromatography of a polyolefinpolymer, comprising the following step: introducing a solution of thepolyolefin polymer into a liquid flowing through a liquid chromatographystationary phase, the liquid chromatography stationary phase comprisinggraphitic carbon, and wherein the polyolefin polymer emerging from theliquid chromatography stationary phase has a retention factor greaterthan zero.
 2. The method of claim 1, where the polyolefin polymer is acopolymer consisting essentially of ethylene and an alpha olefin.
 3. Themethod of claim 2, where the alpha olefin consists essentially of1-octene.
 4. The method of claim 1, where the polyolefin polymer is acopolymer consisting essentially of propylene and an alpha olefin. 5.The method of claim 4, where the alpha olefin consists essentially ofethylene.
 6. The method of claim 1, where the concentration of thepolyolefin polymer in the solution of polyolefin polymer is greater than0.1 milligrams per milliliter of solution.
 7. The method of claim 1,where the liquid chromatography stationary phase consists essentially ofgraphitic carbon.
 8. An improved liquid chromatography method comprisingthe step of introducing a solution of a polyolefin polymer into a liquidflowing through a liquid chromatography stationary phase, the polyolefinpolymer emerging from the liquid chromatography stationary phase with aretention factor greater than zero, the improvement comprising theliquid chromatography stationary phase comprising graphitic carbon. 9.The method of claim 8, where the polyolefin polymer is a copolymerconsisting essentially of ethylene and an alpha olefin.
 10. The methodof claim 9, where the alpha olefin consists essentially of 1-octene. 11.The method of claim 8, where the polyolefin polymer is a copolymerconsisting essentially of propylene and an alpha olefin.
 12. The methodof claim 11, where the alpha olefin consists essentially of ethylene.13. The method of claim 8, where the concentration of the polyolefinpolymer in the solution of polyolefin polymer is greater than 0.1milligrams per milliliter of solution.
 14. The method of claim 8, wherethe liquid chromatography stationary phase consists essentially ofgraphitic carbon.
 15. An apparatus for determining the monomer tocomonomer ratio of a copolymer, wherein the apparatus comprises a hightemperature liquid chromatography unit comprising a graphitic carbonliquid chromatography column, a pump, a polymer solution, and a meansfor an additional fractionation by size exclusion chromatography orasymmetric flow field flow fractionation, added after the fractionationby the graphitic column.
 16. The apparatus of claim 15, wherein theapparatus further comprises a means to increase the temperature of thestationary phase within the column.
 17. The apparatus of claim 15,wherein the apparatus further comprises a gradient composition mobilephase.